Use of electronic sonar systems in boats by fisherman and other boatsmen has become very popular. Such systems are used to measure the depth of the water and/or to recognize the presence of fish or other objects beneath the boat.
Sonar systems involve the propagation and detection of acoustic or sound waves in water. Of all the forms of radiation, sound travels best through water. Both light and radio waves are attenuated to far greater extent than is sound, particularly in turbid water. Because of the relative ease of propagation of sound waves, underwater sound can be readily applied to depth sounding of a body of water.
Typically, sound waves are developed electronically as a single short pulse. This output wave or signal is conveniently generated by an electric circuit oscillator. The resultant electrical energy is converted into acoustic energy by a transducer and is sent out into the water in a cone-like fashion. The signal travels through the water to a target, for example, the bottom of a lake, and some portion of the energy reaching the target is reflected or reradiated back to the source as a sonic echo. Upon return, this echo acoustic signal present in the water is reconverted to an electrical signal, usually including electronic amplification. The speed of sound in water is about 4,950 feet per second and, by carefully timing how long it takes for the echo to return, it is possible to determine the distance between the target and the source.
Most relatively low cost electronic depth finders that are used today by fishermen employ a main battery-operated control box located in the boat and housing an electronic device that creates an electrical signal which travels from the control box through an electrical cable to a transducer device that is placed in the water. Usually a single transducer is used for both transmission and reception. The amplified electrical echo signals are processed in various ways and finally applied to a monitor or display device and may be displayed in a variety of readout modes. The control box may include a volume sensitivity or gain control so that the sound signal may be adjusted loud enough to bounce back an echo even if the water is very deep or the body of water has a soft mud bottom which tends to absorb sound.
Despite numerous prior art attempts to devise convenient depth finding devices for fishermen, these devices have several common drawbacks. Most depth finders are multi-unit, cumbersome devices in which the transducer, display indicator and associated electronics are separate units.
Some prior art sonar units, for example, place the transducer over the side of the boat, attached to a wire or cable. See, for example, U.S. Pat. No. 4,339,811, issued July 13, 1982 to Bednarz et al; U.S. Pat. No. 3,588,795, issued June 28, 1971 to Linardos et al; U.S. Pat. No. 4,122,429, issued Oct. 24, 1978 to Hatai; U.S. Pat. No. 3,564,490, issued Feb. 16, 1971 to Camp. Transducers, so arranged, lack stability and the depth finders are somewhat unreliable in their operation.
In other depth finders, the transducer requires a special mount or bracket. For example, U.S. Pat. No. 3,740,706, issued June 19, 1973 to Joseph, and U.S. Pat. No. 3,752,431, issued Aug. 14, 1973 to McBride, disclose transom mount apparatuses for a transducer. See also, U.S. Pat. No. 3,729,162 issued Apr. 24, 1973 to; U.S. Pat. No. 2,837,727 issued June 3, 1958 to Mayes; U.S. Pat. No. 4,282,590 issued Aug. 4, 1981 to Wingate.
In some prior art depth finder devices, the transducer is connected or mounted in some manner to a trolling motor. Fishing boats often utilize small electric motors which may be bow mounted or transom mounted as a secondary source of power for trolling or positioning. For example, U.S. Pat. No. 3,880,106, issued Apr. 29, 1975 to Farmer, discloses a transducer mounted on the front of a trolling motor casing. U.S. Pat. No. 4,152,690, issued May 1, 1979 to Veatch, teaches a transducer mounted on the shaft of a trolling motor. U.S. Pat. No. 4,737,940, issued Apr. 12, 1988 to Arrington, discloses a transducer mounted within the front bearing cap of a trolling motor. In all these devices, the electronics and depth display are separate units from the transducer and/or trolling motor. Moreover, the depth finder and trolling motor must be operated separately. Thus, the fisherman cannot conveniently and simultaneously troll and depth sound.
The display methods used for coupling a sonar system to the observer are no less important than those used in coupling it to the body of water. The form in which the response of the system is presented for observation determines to a considerable extent the facility with which the information obtained may be utilized. Much can be done by proper choice of the indicating or recording instrument to enhance any characteristics of the signal.
In most prior art devices, the display instrumentation is usually housed in a separate unit connected to the transducer by cable. The display indicators are often difficult to read under many environmental conditions and from locations in the boat remote from the display.
Several kinds of data displays indicating water depths are known. These include a simple meter unit which employs a needle in combination with a dial, a graphic recorder which actually prints out a two-dimensional plot of the bottom showing slopes and drop-offs, a digital read-out which displays numerical values of the depths, or a video display which may be a direct read-out of depths or a graphic representation.
Digital read-outs have become particularly popular since they are readily associated with solid state circuitry. Prior art devices which utilize digital read-out displays include those disclosed, for example, in U.S. Pat. No. 3,588,795, issued June 28, 1971 to Linardos et al and U.S. Pat. No. 4,281,404, issued July 28, 1981 to Morrow et al; U.S. Pat. No. 4,122,429, issued Oct. 24, 1978 to Hatai; U.S. Pat. No. 4,339,811, issued July 13, 1982 to Bednarz et al. Digital read-out displays, however, lack the visual vertical and horizontal displacement information of a graphic recorder.
A single unit depth finder/display indicator has been disclosed in U.S. Pat. No. 4,281,404, issued July 28, 1981 to Morrow et al. This patent teaches a hand held, self-contained depth finding device which is gun-shaped, wherein the transducer and read-out display in the form of a liquid crystal are housed in a single case. One end of the barrel-shaped portion of the device houses the transducer and is immersible in water; the liquid crystal display is housed at the opposite end of the barrel. While such a unit has the advantages of size and compactness, the device has the disadvantages of having to be held in the fisherman's hand partially immersed in the water, and triggered for operation. It is also cumbersome if the fisherman is attempting to operate the trolling motor at the same time.
Despite recognition of the many practical design problems for convenient depth sounding, especially in combination with trolling, proper solution to all these problems in a single device has not been demonstrated in the prior art. None of the prior art devices provides features of single unit construction of the depth finder and the trolling motor which allows simple and convenient simultaneous operation of both devices, single unit construction of depth finder and display instrumentation, or displays of depth information which are both easily readable at a distance and give a pictorial representation of the depth.